By tweeting what, if true, would have been classified information, President Donald Trump may have set a dangerous precedent with his claim Barack Obama ordered his office wiretapped before the election.
Mr Trump alleged in a string of angry messages on Saturday that his predecessor had ordered his New York office be put under surveillance "just before the victory". He called Mr Obama a "bad (or sick) guy" and likened the supposed move to "Nixon/Watergate".
The unsubstantiated claim appeared to have originated in a conservative radio broadcast, later written up on Breitbart, the far-right, Trump-backing website headed until recently by Steve Bannon, now the President's chief strategist.
Mr Trump's early-morning tweets would have been criminal had they been posted by anyone else—and had the claim, denied by Mr Obama, been true—according to a former FBI lawyer.
Matt Olsen, also the ex-director of the National Counterterrorism Centre, told ABC News: "Anyone who would reveal the existence of a wiretap would violate federal law.
"It is against federal law to disclose the existence of a wiretap, whether that wiretap is for criminal purposes or intelligence purposes."
The President is the US' top classification authority.
But if Mr Trump did exercise his powers in this case and leaked the existence of the wiretap, it could weaken his stance against the unauthorised leaks that have been a feature of his presidency so far.
Mr Trump has called sections of the media the "enemy of the American people" over their use of anonymous sources in stories revealing behind-the-scenes details of his administration.
He has repeatedly tweeted about his anger over "illegal leaks".